Vibrator



y 1935. J. MCD. lDE 2000 026 VI BRATOR Original Filed Sept. 14, 193:5

I1? 0671607 J07??? 777. I076 ated magnetostrictively. Vibrators of thischar- Patented May 7, 1935 Divided and this application June 14, 1934,Serial No. 730,566

4 Claims.

The present invention relates to vibrators, and more particularly tovibrators having a low varying or substantially constant frequency withvariations of temperature, and adapted to be operacter are disclosed inUnited States Letters Patent 1,882,397, granted October 11, 1932, toGeorge W. Pierce. The invention includes, also, other vibrators, such astuning forks.

The present application is a division of appli-- cation Serial No.689,493, filed September 14, 1933.

An object of the invention is to provide a new and improved vibrator ,ofthe above-described character. Other objects will be explainedhereinafter, it being understood that it is intended to set forth, bysuitable expression'in the claims, all the novelty that the inventionmay possess.

The invention will be explained in greater detail in connection with theaccompanying drawing, the single figure of which is a diagrammatic viewof a vibrator embodying the present inven-- tion and connected into amagnetostriction-oscillator circuit. 0

, The vibrator is shown at 2, in the form of a rod, but it may have anyother desired shape, as a tube. It is illustrated as positioned axiallyof a magnetic field, here shown as produced by coils 22 and 24. Forsymmetry, one of the coils is positioned on one side of the middle ofthe core 2 and the other on the other side. The coil 22 is connected, inseries with the local battery l0, between the filament or cathode 26 andthe plate or anode 2B, in the output or plate circuit of a vacuum tube30. The coil 24 is similarly connected in the input or grid circuit ofthe tube, between the filament 26 and the grid or third electrode 32.The coils 22 and 24 thus form electrical paths between the filament andthe plate, and between the filament and the grid, respectively. The gridand the plate may, if desired, be spanned by a variable condenser 34, orthe tuning condenser may be connected in parallel with one or the otherof the coils 22 and 24; or, if.the coils are suitably designed, thecondenser may be omitted altogether. An electric vacuum-tube oscillatoris thus provided, as described more fully in United States LettersPatent 1,750,124, granted March 11, 1930, to the said Pierce. As is alsothere stated, the local'battery l8 may serve to supply the platecurrent, as well as to polarize the vibrator. In the illustrativedrawing, polarization is effected by means of a separate winding 35, inseries with a polarizing battery 31. A steady magnetizing or polarizingfield is thus applied, over which the alternating field is superposed.

As is explained in thesaid Letters Patent 1,882,- 397, the frequency ofa particular mode of vibration of a rod or bar is determined by itselasticity, length and density. For some modes of vibration, thefrequency is affected also by the and nearly equal 'in magnitude, to a.

width, thickness, radius, and the like, of the rod or bar. Differentbodies have different magnetostrictive properties. Alloys containingnickel,

chromium, cobalt and'steel, in proper proportions,

some of the alloys have very low, substantially zero, temperaturecoefficients of frequency of longitudinal vibration. It was found thatthe temperature coefficient of frequency is a function of composition,heat treatment, temperature and magnetization. Four compositions werefound which gave temperature coeflicients of the order of one to fifteencycles in a million per centigrade degree, when properly heat-treatedand magnetized. Some of these show large dynamicmagnetostrictiveefiects, so as to constitute powerful magnetostrictivevibrators, and give good frequency stabilization when used in the audiorange and up to about 100,000 cycles per second with a magnetostriction,vacuum-tubeoscillator, such as is disclosed in the said-Letters Patentof the United States 1,750,124, and illustrated in the strictionoscillators, or for oscillators driven in any other way. i

The following considerations will help to an understanding of thepresent invention. Let lbe the length, of the vibrator, D the densi ofthe material of which the vibrator is constituted, a the temperaturecoefficient of linear expansion of this material, b the temperaturecoefficient of Youngs modulus E, and g the temperature coefficient offrequency of longitudinal vibration. By using well known equations forthe velocity of sound 12 in an elastic medium:

If the temperature be permitted to change slight- 1y, it can be shownthat It is obvious from this equation that one way to get a smalltemperature coefficient of frequency is to make alloys for which I) isopposite in sign, Since a is always positive, in metals, and variesinvalue from 1x 10-" to 12X 10* for alloys of iron. nickel and cromium, itis desirable to make alloys for which 12 will be negative in sign and ofthis order f magnitude.

In an alloy containing as per cent nickel, 8 to 10 per cent chromium,and the balance iron, the value of 9 can be made vanishingly small,under suitable magnetic and thermal conditions. It is likewise true, asI-have found, that the 8 per cent and 10 per cent chrorm'um alloys arevery active magnetostrictively and are powerful magnetostrictivevibrators. The addition of about 13 per cent of cobalt to theiron-nickel alloy containing 36 per cent nickel, reduces g to zero.

The temperature coefficient of frequency 9, for any given alloy of thisseries, may vary with temperature, and with the polarizing magneticfield applied to the rod. For all these alloys, g can be changed by heattreatment, such as quenching or annealing. g is thus primarily afunction of composition, although it is, to some extent, in-

financed by heat treatment, magnetization, and temperature.

It is advantageous to give to the alloys about 1 per cent of manganeseas a deoxidizer, to facilitate forging. The impurities should be low, sohigh-grade materials are desirable; for example, electrolytic nickel,cobalt, chromium, and Armco If the natural frequency of vibration of aspecimen rod is measured as a function of temperature, and the frequencyis plotted in a curve against temperature, the temperature coeflicientof frequency is the slope of this curve.

In the experimental work on which this invention is based, the naturalfrequency of the rod was measured by placing it in the coils of a.magnetostriction oscillator, such as is illustrated in the accompanyingdrawing, the frequency of which oscillator the rod was allowed tocontrol. Some harmonic of this frequency (usually the seventh) was madeto produce beats with some harmonic (usually the fifth) of thefifty-kilocycle output from a General Radio, Class C-21-I-I,crystal-controlled, standard-frequency assembly. The differencefrequency was amplified and measured by an audio-frequency meter. Thenatural frequency of the rod could thus. be ascertained with highaccuracy.

Measurements were made with the temperature I of the rod at any desiredvalue between room. temperature and C.

Each rod was measured at four or five different temperatures, and with aseries of various polarizing fields, so that curves were obtained,giving the natural frequency as a function of the magnetic field and ofthe temperature. From these curves, temperature coefiicients could becomputed under various conditions of temperature and magnetization foreach specimen.

. The following were found to be favorable alloy compositionscontainingcobalt: Co 5 per cent. Cr 5 per cent, Ni 39 per cent; Co 4 percent, Cr 8 per cent, Ni 37 per cent. The balance is iron in each case.On the other hand, two groups of alloys, those with 15 per cent cobalt,and those with 12 per cent chromium, determined ascontrol experiments,do not show any coefficients smaller than about -l5 10- A more completetable will be found on page titled, Magnetostrictive Alloys withLow-Temperature Coefiicients of Frequency, Proceedings gg3the Instituteof Radio Engineers, February,

To show also the effect of heat treatment on the variation of frequencywith magnetic field, samples cut from the same rod were measured in thequenched, annealed, and forged conditions.

of my paper, en-- The annealed sample showed 0.6 per cent frequencychange, the forged sample 0.2 per cent change, and the quenched sample0.1 per cent change, as the magnetic field was increased to saturation.This behavior with heat treatment is typical of most of these alloys.

The tests showed that there is less frequency variation with field asthe temperature rises.

The tests showed further that the addition of more than 10 per cent ofchromium or of cobalt to the iron-nickel series (30 per cent to 40 percent nickel) reduces the dynamic magnetostriction effects.

It was demostrated that there is a critical magnetizing field, for eachspecimen, where the temperature coeflicient changes from positive tonegative values, passing through zero. The amount of change in thetemperature coefiicient, as the field varies, was shown tobe large forthe annealed and forged samples and very small for the quenched sample.

By proper choice of composition, the temperature coefficients can bemade too small to measure, or lessthan one part in a million per degreecentigrade, by careful adjustment of magnetic field and heat treatment.Without such adjustment, the coefiicient may be counted upon to be lessthan 20 cycles in a million per centigrade degree.

This research shows that, while the temperature coeflicient may be madenegligible, the magnetic field applied to the rod may cause considerablevariation of the rod frequency. It thus appears that variations inmagnetic field may, in

some cases, be more objectionable than temperature changes. As thetemperature coefiicient varies somewhat with temperature, heattreatment, and magnetic field, it is possible, by arranging the thermaland magnetic conditions, to obtain practically zero temperaturecoeflicient with any 40 of the above compositions. Other compositionsclose to these will have very small coefficients.

The. desirable characteristics for frequency standards to controlmagnetostrictive oscillators are strong magnetostrictive stabilizationof frequency, small temperature coeflicient of frequency, and smalleflect of magnetic field on frequency. The above enumerated alloysdesignated as favorable are practical compositions for applicationsrequiring low temperature coefficient, low magnetic-field coefficient,and excellent stabilizing power, or large dynamic magnetostriction. Byquenching these allows, the magnetic-field coeflicient can be stillfurther reduced without affecting the other desirable properties.

Modifications may be made by persons skilled in the art withoutdeparting from the spirit and scope of the invention, as defined in theappended claims.

What is claimed is:

1. A vibrator having a substantially constant frequency with variationsof temperature and constituted of cobalt, chromium, nickel and iron, anda coil cooperatively related to the vibrator, the relation between thecoil and the vibrator being such that the current flowing through thecoil is subjected to the reaction of the vibrator at a frequency whichresonates with the vibrator.

2. A vibrator having a substantially constant frequency with variationsof temperature and constituted of cobalt, chromium, nickel and iron,with a small percentage of manganese, and a coil cooperatively relatedto the vibrator, the relation between the coil and the vibrator beingsuch that the current fiowing through the coil is sub- 75 jected to thereaction of the vibrator at a frequency which resonates with thevibrator.

3. A vibrator having a substantially constant frequency with variationsof temperature and constituted of 5 parts cobalt, 5 parts chromium, 39parts nickel, and the balance iron, and a coil cooperatively related tothe vibrator, the relation between the coil and the vibrator being suchthat the current flowing through the coil is subjected to the reactionof the vibrator at a frequency which resonates with the vibrator.

4.'A vibrator having a substantially constant frequency with variationsof temperature and constituted of 4 parts cobalt, 8 parts chromium, 37parts nickel, and the balance iron, and a coil cooperatively related tothe vibrator, the relation between the coil and the vibrator being suchthat the current flowing'through the coil is subjected to the reactionof the vibrator at a frequency which resonates with the vibrator.

' JOHN McDONALD mm

